Short-range wireless devices (SRDs) refer to wireless transceivers that support one-way or two-way communication without causing interference with other wireless systems. These devices are widely used across various industries and provide a broad range of services. Common applications include remote control systems in home automation, wireless sensor networks, security alarms, automotive functions such as keyless entry and remote start, and the transmission of voice and video signals. When designing short-range wireless systems, engineers must carefully choose frequencies that operate within unlicensed bands, provided they meet specific technical and regulatory requirements. Table 1 outlines the frequency bands available for SRDs globally.
For global system designs, the 2.4 GHz band is commonly used due to its wide availability and compatibility with multiple technologies. This frequency has become the standard for Bluetooth, Wi-Fi (WLAN), and ZigBee protocols. In addition, the 5.8 GHz band is also utilized in certain wireless phone applications and specific versions of Wi-Fi, such as 802.11a.
However, for applications requiring longer transmission ranges and lower power consumption, frequency bands below 1 GHz are gaining popularity. These bands offer better propagation characteristics and reduced coexistence issues, which help in minimizing power usage—especially important for battery-powered devices. As a result, many low-power wireless systems now target these lower frequency ranges for improved efficiency and performance.
WCDMA, or Wideband Code Division Multiple Access, is a third-generation (3G) mobile communication technology based on the GSM MAP core network and the UTRAN (UMTS Terrestrial Radio Access Network) as its wireless interface. It evolved from CDMA and is recognized as an extension of IMT-2000, offering higher data rates and greater mobility compared to previous generations. WCDMA uses direct sequence spread spectrum code division multiple access (DS-CDMA) combined with frequency division duplex (FDD), with a chip rate of 3.84 Mbps. It supports voice, image, data, and video communication at speeds up to 2 Mbps in local area networks or 384 Kbps in broadband networks. The signal is first digitized and then spread across a wide frequency band. While narrowband CDMA uses a 200 kHz carrier, WCDMA operates on a 5 MHz channel. Currently, WCDMA is licensed to China Unicom.
CDMA2000 is another 3G mobile communication standard, with two main phases: CDMA2000 1x EV-DO (Evolution Data Only), which separates data and voice channels, and CDMA2000 1x EV-DV (Evolution Data and Voice), which integrates both into a single channel. Also known as CDMA Multi-Carrier, this standard was developed by Qualcomm and later adopted by companies like Motorola, Lucent, and Samsung. Originating from the narrowband CDMA One standard, it allows for a smooth upgrade path to 3G with minimal infrastructure changes.
TD-SCDMA stands for Time Division-Synchronous Code Division Multiple Access, one of the three 3G standards approved by the ITU. Unlike WCDMA and CDMA2000, it was developed by China and introduced later. It incorporates advanced technologies such as smart antennas, synchronous CDMA, and software-defined radio (SDR). TD-SCDMA uses time division duplexing, ensuring similar uplink and downlink channel characteristics. Its use of smart antenna technology provides inherent advantages, including interference reduction and improved spectral efficiency. Additionally, it offers flexibility in adjusting the ratio of uplink and downlink time slots, making it ideal for Internet-based applications where downlink traffic is higher. However, this dynamic adjustment adds complexity to network planning and operation.
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